光线投射是非规则数据场体绘制的一种常用方法。它能生成高质量的图形，但开销很大。其原因在于光线与面的求交，特别是与外部面的求交，需要非常大的工作量。本文利用平面多边形扫描算法求取光线与外部面的交点，井利用内部体元和面的相关性，改进了光线与内部面的求交计算，从而减少了运算量，提高了绘制速度。

Ray casting is a useful volume rendering method for visualizing irregular data this method can produc high quality images. However, It is quite time-consuming due to the intensive intersection calculation between rays and cell facets, especially the exterior cell facets. In order to speed up the intersection, computation, an improved method is proposed in the paper by taking the advantages of polygon scan conversion algorithm for the exterior cell facets, and of geometric coherence for the interior cell facets.